Biopsy arc means and the use of the same

ABSTRACT

The invention relates to a biopsy arc intended to be the support of examination needles in connection with computer tomography. The arc is removably secured to the patient&#39;s table and angularly adjustable to be adapted to the direction of the respective section image plane. The arc has a plurality of apertures directed towards the area enclosed by the arc for guiding the examination needles. The arc is made of a material which has an attenuation with respect to X-ray radiation which lies at or below the value exhibited by organic tissue, whereby the arc as well as organs can be brought to appear and stand out together on the section picture in order that a suitable aperture and direction of examination can be selected without risk of disturbing artefacts.

TECHNICAL FIELD

In connection with computed tomographic examinations nowadays often socalled biopsy arcs are used, that is, guiding instruments for insertingproperly and safely examination means, such as sampling needles and thelike, into the patient body concerned. Usually such biopsy arcs areprovided with complicated adjustment means for directing the needles,and they require that the operating personnel be thoroughly trained inorder that said means be used in an appropriate manner. Furthermorethere are very often a risk of so called disturbing artefacts caused bythe structure of the devices when these come into the vicinity of thesection image. In examinations of the said kind it is thus veryimportant that the occurring section images of the patient bodyconcerned are not disturbed by structural material attenuating theradiation, as the contents of the images can easily be misinterpreted insuch cases.

PRIOR ART

In this technical field there are a plurality of known designs, as canbe seen from the patent literature. As an example the German PublicationDE 32 05 915 can be mentioned. The device shown in this paper includesan arc which encloses substantially 270° of a circle and is secured to apatient's table. On the arc, which is provided with indicia, there is aslider to be slidably pushed along the arc. The slider includes a needlecarrier which is movable about an axis and thus able to be turned in theplane of the arc. After a section image of a body under examination hasbeen studied and the organ to be examined or punctured has beenlocalized, the approximate insert angle of the needle is determined,also the depth of insertion, after which the needle carrier is set onthe arc in the estimated position and approximately directed. Then theneedle is inserted into the patient and loosened from the arc in orderthat a check picture be taken and the needle position obtainedevaluated. Should positioning not be carried out exactly as intended theneedle has to be pulled out, a new directing operation be carried outand the needle be inserted again. This is of course not satisfactoryneither with respect to the examination nor to the patient.

The German Patent Specification DE 33 39 259 discloses an arcarrangement provided with some radial apertures through which guidemeans can be inserted for, in this case, drilling. The arrangement hasno direct bearing on computed tomography but still it is mentioned asrepresenting prior art guiding instruments.

As an example of usually occurring biopsy arc arrangements reference ismade to the U.S. Pat. Nos. 4,350,159 and 4,463,758. These arrangementsboth include advanced structures for adjusting needles when carrying outexaminations of the said type in connection with computed tomography. Ascan be clearly seen from the structure of these arrangements verydisturbing artefacts can arise in the tomographic pictures if parts ofthe structures concerned should enter into the respective sectionpicture.

Thus there is a need of a simple and safe method of determining theposition as well as the penetration depth of an examination needlewithout it being necessary to resort to either intricate trigonometriccalculations or complicated apparatus adjustments.

SUMMARY OF THE INVENTION

The present invention solves the problem mentioned above in a verysimple and appropriate manner. A biopsy arc according to the invention,in particular for computed tomography, is provided with a plurality ofapertures directed towards the area within the arc, the arc beingmounted in such a way that it can be angularly set for adjustment of theplane of the arc to a plane of image section in the computed tomographicapparatus. Furthermore, the arc should be such as to exhibit such anattenuation of the radiation concerned which is equal to or less thanthat exhibited by organic issue. The arc will then form part of therelated section image, whereby the directions of the apertures will beidentifiable. Hereby it is possible, in order to select to suitable pathfor inserting an examination means, to select a suitably directedaperture through which said means can be inserted. Expediently theapertures have such a diameter that they can receive guiding sleeves forthe examination means concerned, such as a needle or the like. Thanks tothe fact that the arc has apertures of a comparatively large size theseapertures will be clearly depicted in the section image as channels ofgiven directions. Hence, it is comparatively simple to select anaperture for inserting an examination means if, in the image, thedirection of the aperture agrees with the desired path of insertion.Contrary to what is occurring in known techniques the biopsy arc isallowed to remain in the path of the X-ray beam creating the imagesection, in order to render it possible to utilize the arc configurationin the section image in connection with the examination contemplated.

The characterizing features of the present invention appear from thepatent claims following the specification.

The invention will be described in greater detail with reference to theaccompanying drawings which illustrate embodiments of the invention.

IN THE DRAWINGS

FIG. 1 shows a biopsy arc in accordance with the invention inperspective and mounted on a patient base.

FIG. 2 shows said arc partly in section.

FIG. 3 shows a lateral view of the arc.

FIG. 4 shows a guiding sleeve and an examination needle inserted in thesame.

FIG. 5 shows a tomographic section picture with the biopsy arc outlinedtherein.

FIG. 6 shows essentially the same picture as FIG. 5 but with a computerdesigned reference grid applied.

FIG. 7 shows a biopsy arc design with chordally directed apertures only.

FIG. 8 shows a biopsy arc having radially directed apertures only.

DISCLOSURE OF EMBODIMENTS

The biopsy arc 1 shown in FIG. 1 is connected, by a detachable supportmember 2, with guide rails 3 or either side of a patient's table 4. Thebiopsy arc is provided with a plurality of apertures 5. Patient's table4 is insertable in a computed tomography installation 6, in a manner notto be described in detail.

As seen from FIG. 2 there are, on one half of the biopsy arc, a numberof radially extending apertures 7 which are directed towards a centraltarget point 8. On the opposite side of the arc 1 there are a number ofapertures 9 parallel with each other and chordally directed.

As can be clearly seen in FIGS. 2 and 3 the support member 2 of thebiopsy arc 1 is provided with a slide 10 intended to run along therespective side rail 3 and to be locked to the rail in desired positionsby means of set screws 11. The biopsy arc 1 itself can be clamped by itslegs or shanks against the respective slide 10 by means of a plate 12having slits 13, 14 through which retaining screws 15, 16 are inserted.By the slit arrangement 13, 14 the biopsy arc 1 can be adjusted invarious angular positions in relation to the patient's table 4, asindicated by the double arrow 17. To this end indicia 18 are provided onthe side of each plate 12. The disengageable clamping of the biopsy arcshanks by means of the plates 12 and the retaining screws 15, 16 bringswith it that a certain adjustment of height can be performed in order toadjust to the body of the patient concerned, as indicated by the doublearrow 19. On the biopsy arc 1 itself indicia 20 are provided on eachshank.

To make it possible to guide and secure an examination needle in thedesired position in any of the apertures 5 a sleeve 21 having a flange22 is provided. The sleeve is made with a central through hole, throughwhich a needle 23 can be inserted, as shown in FIG. 4. Suitable a socket24 is pushed onto the needle, to be secured to the needle by a setscrew. Hereby an insertion stop is provided, whose position is adjustedin accord with the required length to which the needle is to be insertedinto the patient's body. The device shown in FIG. 4 has the advantagethat only the needle 23 and the sleeve 21, 22 need be sterilized betweenvarious examinations of a patient, thus not the arc proper.

The biopsy arc 1 is made of a material having a density and propertiesin relationship to the X-ray radiation concerned which can be ranked inthe same category as organic tissue density, that is, the density oftissue occurring in a patient's body. The density of tissue generallylies between 40 and 150 Hounsfield units, abbreviated H-units. Toclarify the meaning of H-units the following may be pointed out. As itis not practical to work with μ-values in computed tomographic scanninga new scale of values related to the linear attenuation coefficient havebeen defined by Hounsfield. The unit in this new scale is abbreviated H(meaning Hounsfield).

The scanning device used by Hounsfield operated at 120 kV with analuminium filter of thickness 4.5 mm and a water container 27 cm thick.Under these particular conditions it was found that the μ-value of waterwas 0.19 cm⁻¹ (i.e. 0.19 per cm), which is equivalent to the μ-value ofwater measured by a monocromatic beam of 73 keV. In consequence herewitha Houndsfield unit for a substance `x` is defined by the followingequation ##EQU1## or H=5263 μx-1000

It is important to know that the above equation is based on theprerequisite that 10 H-units correspond to a change of 1% of μx, inrelation to the μ-value of water.

From the above formula it can be calculated that H of water is 0 whilethe value of air is -1000 and that the value of dense bone tissue canraise up to +3095 H . A scanning system can thus handle 4096 differentH-values for each image element. H-values of some anatomic substancesand synthetic materials are shown in the table below.

    ______________________________________                                        Dense bone tissue     up to 3095                                              Bone                  200-1000                                                Teflon                950                                                     Delrin                365                                                     Bakelite              264                                                     Perspex               125                                                     Lexan                 105                                                     Nylon                 89                                                      Dense tumour tissue   50-90                                                   Coagulated blood      55-75                                                   Brain tissue (grey)   36-46                                                   Brain tissue (white)  22-32                                                   Blood                 12                                                      Water                 0                                                       Polystyrene           -28                                                     Fat                   -100                                                    Air                   -1000                                                   ______________________________________                                    

Thus the material density of the biopsy arc must not exceed such valuesthat artefact disturbances can arise in the image concerned. Preferablythe material should have a value below 200 H.

Polyamide plastics, having a H-value about 80, is satisfactory for mostpractical purposes. What is essential is the feature that the arc standsout in the section image so that the respective aperture and itsdirection can be identified.

USE AND FUNCTION OF THE ARRANGEMENT

Examination of a patient while using the biopsy arc according to theinvention is conducted in the following way:

In modern computed tomographic installations there are laser light beamsfor positioning so that the section plane of the scanning unit can beprojected on the patient's body, after which pencil markings can bemade. The biopsy arc is then secured to the patient's table 4 andangularly adjusted in accordance with the markings drawn so that theplane of the arc will coincide with the plane of the image section ofthe computed tomograph. When the patient's table 4 is again introducedinto the tomograph 6 and the requested section pictures are taken, thearc with its apertured channels will be outline in each picture togetherwith the organic tissues occurring in the image section, in a way asillustrated in FIG. 5. It is assumed that in FIG. 5 a vertebra 25 withribs 26 belonging thereto are outlined in the picture. Within the areadesignated 27 the image of swollen organ stands out which, for example,is to be punctured. Now, the question is to insert the puncturing needleto this organ in such a way that no adjacent organs are damaged. So inthis case one of the apertures 7 is selected which as to its directionseems to be the suitable one for reaching the said organ 27, asindicated by the dashed line.

However, in order to make it possible to determine the path and depth ofneedle penetration a reference grid 28 having a center line 29 isapplied on the monitor image obtained, as seen in FIG. 6, said centerline passing in this case through the spinal cord portion 30 of thevertebra 25. The reference grid is used to find the point 8 towardswhich the radially directed channels converge, in doing which there ismarked on the center line 29, which coincides with the radial directionof the central aperture of the arc, the point which forms the targetpoint of all radial apertures 7, that is, point 8 in FIG. 2. Startingfrom said point lines can then be drawn towards apertures 7 in order toselect a suitable path of insertion and the associated needle. Thisreference grid is divided into such measuring units that they aredirectly, or by computer, convertable to the penetration depth of thepuncturing needle concerned. In practice it is advisable to design thesoftware of the computer such that measures of the depth of penetrationand also of the needle socket length can be readily read by cursorcontrol. As have been previously pointed out in connection with FIG. 4,the length of insertion is set by means of the socket 24 which abuts theflange 22 of the sleeve 21 when the proper length of the needle has beeninserted.

Thus when the position of an organ 27 has been established a suitableaperture in the arc is selected in accordance with the above, i.e. anaperture having the correct direction towards the organ. The needlelength is adjusted as described, after which the patient's table 4 withthe patient is pulled out from the computed tomograph, and with the arcin its set position the aperture 7 concerned is used for inserting ofthe sleeve 21 and said needle 23. The needle is inserted to the depthaimed at and the patient can now be introduced again with the table 4into the computed tomograph so that a picture for checking can be taken.It should be noted that it is not necessary to remove the arc whenchecking the position of the needle, as the arc, the needle, as well asthe guide sleeve 21 can be allowed to appear in the section image, andthis without any disturbing artefacts arising. The result of the organpuncture can also be checked in this manner with all settings unchanged.

If, in viewing the section image, it is seen that the radial apertures 7cannot be used for the necessary measure, the biopsy arc can readily beturned by its shanks being pulled out from their engagement with therespective support member 2 and turned 180° so that the chordiallydirected apertures 9 are now located on the side where the organ 27 issituated. A suitable aperture having the requested position anddirection can now be selected for the examination intended. In this caselines parallel with the line 29 of the reference grid 28 will now beessentially parallel with the direction of needle introduction,rendering it easy to read the depth of penetration. As can be seen theuse of a biopsy arc according to the invention involves only a smallnumber of manipulation steps and calculations as compared with knowndesigns. Thanks to the feature that the arc can be allowed to form partof the examination image without creating disturbing obstacles and thatit is possible to determine in a simple way from this image aperturesand positions for inserting the needle, contribution is given to aperspicuity which is very valuable in the practical work involved incomputed tomographic examinations. In view of its simple structure andthe perspicuous way the arc is used its handling will be very easy tolearn.

In some connections it could be advisable to use arcs which e.g. havecordally directed apertures only. Such a structure is shown in FIG. 7.

Likewise it could be advisable sometimes to use an arc which hasthroughout radial apertures directed towards a central target point.Such a structure can be seen in FIG. 8.

As a matter of course a plurality of designs can be contemplated withinthe scope of the invention where, for instance, several different typesof apertures 5 can occur. For example, such structures can be conceivedwherein differently directed apertures are located adjacent one anotheror in the interspace between apertures. Thus e.g. every second aperturecan be radially directed, such as apertures 7, and every secondchordally directed, as apertures 9. In a manner suitable for certainpurposes groups of apertures can be distributed along the arc and havevarious directions. Of course also arrays of apertures adjacent eachother can be provided, differently directed. Such solutions can bevaluable if it is desirable to select an aperture having a very specificdirection, in doing which the biopsy arc can be angularly tilted throughthe plane of the image section according to arrow 17 in order todetermine the desired aperture.

The biopsy arc can also be secured to another base member than thepatient's table shown. For example, a separate base slab can be usedwhich can be placed on the patient's table and retained thereon by thepatient resting on the slab by his own weight.

We claim:
 1. A biopsy arc system for computed tomography comprising anarc which is adapted to be mounted archwise above a body that is to beexamined, said arc being adjustably secured to a base member, the arcbeing provided with a plurality of apertures having axes which aredirected towards the area within the arc, the arc being secured to thebase member in such a way that it can be angularly adjusted in order toadapt a plane of the arc to an image section plane, the arc having aradiation attenuation coefficient which is essentially the same orsmaller than a radiation attenuation coefficient exhibited by an organictissue so that the arc will form a part of the associated image sectionplane whereby an axis of at least one of the apertures is identifiablein order that a suitable path may be selected for inserting anexamination means through a selected aperture.
 2. A biopsy arc systemaccording to claim 1, wherein the apertures have a diameter larger thanthat of said examination means and wherein said arc includes a sleevewhich is located in one of said apertures in the arc for receiving saidexamination means.
 3. A biopsy arc system according to claim 1, whereinone group of the apertures has axes which are radially directed towardsa point within the area bounded by the arc and a second group ofapertures has axes with a chordal orientation within the arc, the arcbeing removably secured to a base member so that said arc, whenloosened, can be turned and re-secured for adjustment to a properaperture for an examination being performed.
 4. A biopsy arc systemaccording to claim 1, wherein said arc comprises shanks on each end ofthe arc which are clamped to slides running along side rails mounted oneither side of the base member.
 5. A biopsy arc system according toclaim 4, wherein a plate is pivotally mounted on said slide and whereinsaid arc includes means for clamping the respective shank of the arcbetween the plate and the respective slide.
 6. A biopsy arc systemaccording to claim 1 wherein the arc is made of a material which has anattenuation coefficient with respect to X-ray radiation of 200 H orless.
 7. A biopsy arc system according to claim 6, wherein the arc ismade of polyamide plastic.
 8. A biopsy arc system according to claim 1,wherein the arc is made of a material which has an attenuationcoefficient with respect to X-ray radiation of 80 H or less.
 9. A biopsyarc according to claim 1, wherein the arc is made of a material whichhas an attenuation coefficient with respect to X-ray radiation of 70 Hor less.
 10. A biopsy arc according to claim 1, wherein the arc is madeof a material which has an attenuation coefficient with respect to X-rayradiation of 125 H or less.
 11. A frame for use in computed tomography,comprising:an arc comprising a material having a radiation attenuationcoefficient which is less than a radiation attenuation coefficient ofsome organic tissue that is to be examined; a plurality of aperturesarranged in the arc having axes directed towards an area under the arc;and means for angularly adjusting the arc so that at least some of saidaperture axes coincide with a section plane of a tomographic image inorder to form a part of said tomographic image.
 12. A frame according toclaim 11, further comprising a sleeve arranged in one of said aperturesfor receiving a biopsy needle.
 13. A frame according to claim 11 whereinthe axes of some of said apertures are directed radially toward a centerof said arc.
 14. A frame according to claim 11 wherein the axes of someof said apertures are directed chordially on said arc.
 15. A frameaccording to claim 11 wherein the axes of some of said apertures aredirected radially toward a center of said arc and the axes of other ofsaid apertures are directed chordially on said arc.
 16. A frameaccording to claim 11 wherein said arc further comprises two shankswhich are slideably connected to a base member.
 17. A frame according toclaim 11 wherein said attenuation coefficient with respect to X-rayradiation is less than or equal to 200 H.
 18. A frame according to claim11 wherein said attenuation coefficient with respect to X-ray radiationis less than or equal to 80 H.
 19. A frame according to claim 11 whereinsaid arc material comprises any polyamide plastic.
 20. A frame accordingto claim 11, wherein said attenuation coefficient with respect to X-rayradiation is less than or equal to 70 H.
 21. A method of performing abiopsy, comprising the steps of:providing the biopsy arc of claim 1making a tomographic image showing a plurality of radially directedapertures in a frame, said image also showing a reference pointcorresponding to an intersection of each of the axes of said apertures;selecting an appropriate aperture for guiding a biopsy needle by drawinga line from said reference point through a target point on said image toan appropriate one of said apertures; determining a depth of penetrationfor said biopsy needle according to a distance from said appropriateaperture to said target point; and penetrating said biopsy needlethrough said appropriate aperture to said target point.
 22. A method ofperforming a biopsy, comprising the steps of:providing the frame for usein computed tomography of claim 10; making a tomographic image showing aplurality of apertures in a frame; selecting an appropriate aperture forguiding a biopsy needle by drawing a line along an axis of one of saidapertures to a target point; determining a depth of penetration for saidbiopsy needle according to a distance from said appropriate aperture tosaid target point; and penetrating said biopsy needle through saidappropriate aperture to said target point.